It is known to heat air in a space being ventilated by admitting heated air to the space through venturi diffusers which also draw in air from the space, mix it with the heated air and pass the mixture to the space to provide ventilating air at a desired temperature.
However, this previous proposal has the disadvantage that there is a large temperature drop of the heated air, and also a large and therefore costly means such as a fan is required for passing the heated air to the venturi mixer(s).